The present invention relates to solid electrolytic capacitors to be used in various electronic devices, and it also relates to a method of manufacturing the same capacitor.
A conventional solid electrolytic capacitor uses a porous sheet of bulb-metal such as aluminum and tantalum as its electrode. To be more specific, a single face in a thickness direction of the porous sheet of bulb-metal or a core section in the middle of the sheet is used as the electrode. A dielectric film is formed on a surface of the porous section of this bulb-metal sheet, and a solid electrolyte layer such as functional polymer is formed on the dielectric film. On this solid electrolyte layer, a current collecting layer is formed, and on top of the current collecting layer, an electrode layer made of metal is formed, so that a capacitor element is constructed. Capacitor elements, each same as the capacitor element are layered, and the electrodes or electrode-layers of the respective capacitor elements are lumped together and coupled to an external terminal. An outer package is prepared for the capacitor elements such that the external terminal comes outside the package. The conventional solid electrolytic capacitor is thus structured.
The conventional solid electrolytic capacitor discussed above allows increasing its capacitance or lowering an equivalent series resistance (ESR); however, it needs to be mounted on a circuit board via the external terminal as a general capacitor needs to be.
Similar to semiconductor components, the solid electrolytic capacitor mounted onto a circuit board incurs large ESR and equivalent series inductance (ESL) in the circuit because of the presence of lengths of the terminals and the wiring. The responsiveness of such a solid electrolyte capacitor to a high frequency is obliged to lower.
Japanese Patent Application Non-Examined Publication No. 2001-307955 discloses a thin solid electrolytic capacitor which is expected to overcome the foregoing problem. This capacitor has an anode and a cathode alternately arranged on its single face so that components such as semiconductor devices can be mounted thereon directly for reducing the ESR and ESL.
However, the direct mounting of semiconductor components and the like on the capacitor applies stress onto the terminals, so that the capacitor needs strength strong enough to this stress. In the case of placing the capacitor just beneath the semiconductor components, the capacitor needs to operate in an atmosphere where a temperature is higher than the conventional one.
A solid electrolytic capacitor of the present invention includes the following elements:
a bulb-metal sheet having a porous section formed at least on its first face;
a dielectric film formed on this porous section;
a solid electrolyte layer formed on the dielectric film;
a current collecting layer formed on the solid electrolyte layer;
a through-hole electrode conductive to the current collecting layer and extending through the bulb-metal sheet outside a second face opposite to the first face,
an insulating film that isolates the through-hole electrode from the bulb-metal sheet;
a first connecting terminal provided on the second face and coupled to the through-hole electrode;
a second connecting terminal provided on the second face and insulated from the through-hole electrode and conductive to the bulb-metal sheet; and
a reinforcing plate bonded to the current collecting layer.
A method of manufacturing the solid electrolytic capacitors discussed above includes the steps of:
(a) forming a porous section on a first face of a bulb-metal sheet;
(b) forming a dielectric film, a solid electrolyte layer, and a current collecting layer on the porous section;
(c) providing the bulb-metal sheet with a through-hole;
(d) forming an insulating film on an inner wall of the through-hole and a second face opposite to the first face of the bulb-metal sheet; then
(e) forming a through-hole electrode in the through hole for being coupled to the current collecting layer;
(f) forming a cathodic electrode layer on the current collecting layer for being conductive to the through-hole electrode;
(g) forming an opening at a given place on the insulating film;
(h) forming connecting terminals on the opening and the through-hole electrode respectively; and
(i) bonding the cathode layer to the reinforcing plate.